Ionization gauge head with reduced electronic desorption



INVENTOR. 9 LQ L A ril 21, 1970 J. GROSZKOWSKI IONIZATION GAUGE HEAD WITH REDUCED ELECTRONIC DESORPTION Filed Feb. 16, 196B .INII.

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3,508,099 IONIZATION GAUGE HEAD WITH REDUCED ELECTRONIC DESORPTION Janusz Groszkowslri, Ul. Nowowiejska 22/7, Warsaw, Poland Filed Feb. 16, 1968, Ser. No. 706,136 Int. Cl. Gtlln 27/62; Htllj 7/16, 41/00 US. Cl. 313-7 11 Claims ABSTRACT OF THE DISCLOSURE An ionization gauge head having an anode constituted by two anode elements in the form of cages at different potentials placed in a vacuum adjacent a cathode to minimize the flow to the collector of ions being electronically desorbed.

BRIEF SUMMARY OF THE INVENTION The invention relates to an ionization gauge head with reduced electronic desorption.

In known ionization gauges based on the principle of measuring ionic current intensity, in the range of highest vacuum there occurs a phenomenon of so-called electronic desorption. This phenomenon consists in that the electron current serving for ionizing the gases in the head upon arriving at the anode causes the ionization of the gases which are desorbed and are present on the surface of the anode. These ions are collected together with those formed in the free space of the head by the ionic current collector. As the surface gases are not adequately representative of the vacuum conditions, the phenomenon creates measuring errors, which increase as the pressure is lowered, since the ion current formed in the free space of the head decreases more rapidly than that of the surface ions.

In order to counteract this harmful phenomenon, there is provided according to the present invention an ionization gauge with reduced electronic desorption, in which, instead of a single anode, two anodes are employed at different potentials (positive relative to the cathode). The anodes are constituted as bars arranged in the form of concentric cylindrical cages. The electrons emitted by the cathode arranged outside of the anodes enter the cage Where they cause ionization of the gases and the formed ions are collected by a collector of suitable negative potential.

In order that the ions, formed by the bombarding electrons, on the surface of the anode bars do not reach the collector, the inner anode is supplied with a lower potential than the outer anode. Thus the ions from the surface of the bars of the outer cage are directed against the bars of the inner cage, and consequently the current of these ions incoming to the collector becomes considerably reduced. The ionization formed on the bars of the inner cage is substantially Weaker, as the electron current flowing towards this cage is considerably less intensive than that flowing towards the outer cage, which is at the higher potential.

Through the choice of distance, pitch and thickness of the bars, and the potentials of the cages, the number of ions formed by the surface ionization and flowing to the collector will be significantly reduced in comparison with the number of ions of this kind present in an ionization head with a single anode.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a longitudinal section of an ionization gauge head with reduced electronic desorption; and

FIGURE 2 shows a modification of the structural design of the anodes.

" United States Patent 3,58,.d99 Patented Apr. 21, 1970 ice DETAILED DESCRIPTION The ionization gauge head according to the invention consists of a cathode 1, two concentric anodes 2 and 3 constituted for example by bars arranged in the form of cylindrical cages, and an ion collector 4 located inside the anodes as shown in FIG. 1, or outside the anodes opposite an orifice in the bottom thereof as shown in FIG. 2. The anodes shown in FIG. 2 form a single cage which, however, is composed of two parts electrically isolated from each other, although they define a common cylinder with generatrices and bases lying in a common plane.

In the sectional view of FIG. 2, the bars of the cage of one anode is shown by dots, and the bars of the second one is shown by circles. The system of the electrodes of the head is installed in a glass bulb 5 or in a metallic casing, and they may also be used in a vacuum system Without a covering.

The bars have been shown in the disclosed embodiments with equal diameter and spacing, but it is also pos sible to modify the sizes of the bars and their spacing, as those skilled in the art will readily understand.

What is claimed is:

1. An ionization gauge head with reduced effect of electronic desorption, comprising a cathode, an anode and an ion collector located in a vacuum, said anode consisting of two anode elements in the form of cages of different potentials to resist the admittance by the collector, of ions being electronically desorbed.

2. An ionization gauge head as claimed in claim 1, in which said cages of the anode elements lie in a single common surface.

3. An ionization gauge head as claimed in claim 1, in which one anode cage is arranged inside the other.

4. An ionization gauge head as claimed in claim 1, in which said cages are constituted of spaced bars.

5. An ionization gauge head as claimed in claim 4, wherein said cages are cylindrical.

6. An ionization gauge head as claimed in claim 4, wherein one cage is concentric and within the other, the inner cage being at a lower potential than the outer cage.

7. An ionization gauge head as claimed in claim 6, wherein said collector extends coaxially within the cages.

8. An ionization gauge head as claimed in claim 5, wherein said bars of said cages define a common cylinder.

"9. An ionization gauge head as claimed in claim 8, wherein said common cylinder has a base with a space therein, said collector being outside said cylinder in the region of said space.

It). An ionization gauge head as claimed in claim 3, wherein the outer anode cage is at a higher potential than the inner anode cage.

11. An ionization gauge head as claimed in claim 9 wherein said space is located on the axis of the common cylinder, said collector extending along the axis of said common cylinder.

References Cited UNITED STATES PATENTS 3,001,128 9/1961 Nottingham 324-33 3,357,903 12/1967 Lawrence 324-33 X 3,394,286 7/1968 Brock 3137 X JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R. 324-33 

